Apparatus for measuring the potential of a transmission line conductor

ABSTRACT

Self contained radio transmitting state estimator modules are mounted on power conductors on both sides of power transformers in electrical substations and on power conductors at various places along electrical transmission lines. They are electrically isolated from ground and all other conductors. These modules are capable of measuring current, voltage, frequency and power factor (or the fourier components thereof) the temperature of the conductor, and the temperature of the ambient air. The modules transmit these parameters to local receivers. The receivers are connected by an appropriate data transmission link, to a power control center which allows determination of the state of the power system. Appropriate control signals are transmitted back to the electrical switchgear of the system to bring it to the appropriate optimum state. Direct local control may also be effected, for example, the prevention of overloading a transformer. A &#34;donut&#34; state estimator module comprises a novel hot stick operated hinge clamp and a novel voltage sensor which measures the current between an isolated capacitor plate and ground. The donut measures the fourier components of voltage and current over a number of cycles and transmits the components to the local receiver. The local receiver derives the desired electrical measurements such as voltage, current, power factor, power, and reactive power and transmits them to local or remote control stations. Up to 15 donut modules may transmit on a single channel to a single local receiver. Each transmits at intervals which are an integral number. The intervals between transmissions of all donuts do not have a common factor and the average interval is the desired transmission rate. Each donut uses the zero crossover of current of its conductor to establish its transmission interval. The system is self-calibrating using known reference signals within the donut module.

This is a divisional of co-pending application Ser. No. 484,681 filed onApr. 13, 1983.

RELATED APPLICATION

This application is related to the prior U.S. patent application ofHoward R. Stillwel and Roosevelt A. Fernandes entitled TRANSPONDER UNITFOR MEASURING TEMPERATURE AND CURRENT ON LIVE TRANSMISSION LINES, U.S.Pat. No. 4,384,289, issued May 17, 1983, which application isincorporated herein by reference.

TECHNICAL FIELD

This invention relates to a system and apparatus for monitoring andcontrol of a bulk electric power delivery system. More particularly itrelates to such systems employing transmission line mounted radiotransmitting electrically isolated modules, preferably mounted on allpower conductors connected to both the primary and secondary sides ofeach power transformer to be monitored, on the highest temperatureportions of transmission lines, and at intervals through the powerdelivery system. When so attached the modules form the basis for adynamic state estimation for real-time computer control of an electricpower delivery system.

Each module takes the form of a two piece donut that may be hot stickmounted on a live conductor utilizing a novel hinge clamp and novel hotstick tool.

Novel voltage measuring and fourier component measuring apparatus and anovel common channel unsynchronized transmission system are disclosed.

BACKGROUND ART

Various power line monitored sensors have been disclosed in the priorart. For example, see U.S. Pat. Nos. 3,428,896, 3,633,191, 4,158,810 and4,268,818. It has been proposed to use sensors of this type and of thegreatly improved form disclosed in the above-identified Stillwel andFernandes application for dynamic line rating of electrical powertransmission lines. See for example, papers numbered 82 SM 337-0 and 82SM 378-8 entitled DYNAMIC THERMAL LINE RATINGS, PART I, DYNAMIC AMPACITYRATING ALGORITHM; and, DYNAMIC THERMAL LINE RATINGS, PART II, CONDUCTORTEMPERATURE SENSOR AND LABORATORY FIELD TEST EVALUATION; paperspresented at the Institute of Electrical and Electronic Engineers P.E.S.1982 summer meeting. These papers are incorporated herein by reference.However, the full potential of this new technology has not beenrealized.

Today, for control and protection, power supply to and from anelectrical substation over various transmission lines is monitored byseparate devices (current transformers, potential transformers andreactive power transducers) for measuring electrical potential, powerfactor and current in the conductors of the transmission line and theconductors connected to substation power transformers. Thesemeasurements are transmitted in analog fashion by various wires to acentral console at the substation where their values may or may not bedigitized and sent to a central station for control of the entire powersystem. The wiring of these devices is difficult and expensive, andevery excess wire in a substation presents an additional electricalshock hazard or an induction point for electromagnetic interference onprotection/telemetry circuits. Furthermore, when a failure occurs, thesesensor lines may be abruptly raised to higher voltages, thus increasingthe possibility of shock and failure in the measurement system.

The high cost of capital, uncertain power utility load growth trends,coupled with increasing constraints in acquiring and licensing newfacilities including right-of-way for transmission lines make greateruse of existing power delivery facilities (remote generating stations,the EHV bulk power network, subtransmission and distribution facilities)a paramount consideration. With deferrals that have occurred in newgeneration and power transmission facilities, all elements of the powersystem will be strained to a greater degree than in the past. In orderto maintain current reliability levels under these conditions,additional real-time monitoring will be required to assist the dispatchoperator and other bulk network functions conducted through a modernPower Control Center.

Some of the functions is a hierarchical modern Power Control Center,operating through Regional Control Centers down to the distributionlevel, that require a real-time Supervisory Control and Data AcquisitionSystem are as follows:

1. State Estimation

2. On-Line Load Flow Detection

3. Optimum Power Flow Control for Real and Reactive Power Dispatch

4. Security (i.e. Stability) Constrained Economic Dispatch

5. Contingency Analysis

6. Automatic Generation Control and Minimum Area Control Error

7. Dynamic System Security Analysis

8. Energy Interchange Billing

9. System Restoration After an Emergency

10. Load Shedding and Generation Redispatch

11. Determination of Effects of Voltage Reduction and Real and ReactivePower

12. Synchronization of System Load Profiles to validate various computermodels and to provide snap shots of maximum, minimum loads, peak dayreal and reactive powers on lines and equipment

13. Maintain Power Delivery Quality Including Harmonic Content forCritical Loads and Power Factor

14. Limit checking of voltage, line thermal loadings and rate of changeunder contingency conditions

15. Protective Relaying.

The key parameters that require measurement for a modern Power ControlCenter State Estimator and On-Line Load Flow that provide the input database for the various functions listed above are:

Line and Transformer Bank or Bus Power (MW) Flows

Line and Transformer Bank or Bus Reactive Power (MVAR)

Flow

Branch Currents (I), Bus Voltage and Phase Angles

Bus MW and MVAR Injections

Energy (MWh) and Reactive Energy (MVAR-h)

Circuit Breaker Status

Manual Switch Positions

Tap Changer Positions

Frequency (f)

Protective Relaying (Differential Currents, etc.)

Operation

Power Line Dynamic Ratings Based on Conductor Thermal

(Temperature) Limits or Sag

Ambient Temperature/Wind Speed

Line and Equipment Power Factors

Sequence-of-Events Monitoring

One of the major problems in implementing a modern Power Control Systemis to add instrumentation throughout the bulk transmission network atExtra High Voltage (up to 765 kV) line voltages and at distributionsubstations and feeders. This must be done wihout disrupting existingoperations of equipment and facilities that are largely in place.Another requirement is to avoid adding too many transducers that mightalter the burden on existing current transformers and degrade accuracyof existing metering or relaying instrumentation.

The toroidal conductor State Estimator Module and around stationprocessor, receiver/transmitter of the present invention eliminates thenecessity for multiple wiring of transducers required with conventionalcurrent and potential transformers and collects all the data requiredfrom lines and station buses with a compact system. The inventionresults in significant investment, installation labor and time savings.It completely eliminates the need for multiple transducers, hard-wiringto current transformers and potential transformers and any degradingeffects on existing relaying or metering links. The system can beretrofitted on existing lines or stations or new installations withequal ease and measures:

Line Voltage

Power Factor or Phase Angle

Power Per Phase

Line Current

Reactive Power Per Phase

Conductor Temperature

Ambient Temperature

Wind Speed

Harmonic Currents

Frequency

MW-h and MVAR-h (processed quantities)

Profiles of above quantities from stored values The state-estimator datacollection system described in this application enables power utilitiesto implement modern power control systems more rapidly, at lower costand with considerable flexibility, since the devices can be moved aroundusing hot-sticks without having to interrupt power flow. The devices canbe calibrated and checked through the radio link and the digital outputcan be multiplexed with other station data to a central processor viaremote communication link.

Many problems had to be overcome to provide an electrically isolatedstate estimator module that can be hot stick mounted to energizedconductors including the highest used in electrical transmission.

Among these were: The design of a positive acting mechanism for hingingthe two parts of the module and securely clamping and unclamping themabout a live conductor while they were supported by a hot stick.Measurement of the voltage of the conductor in a self-containedelectrically isolated module. The desire to make any electricalmeasurements with a necessarily small and light module and commonutilization of a single radio channel by the up to 15 modules whichmight be required at a single substration.

Such hot stick activated hinge and clamp mechanisms do not exist in theprior art. The voltage transformers and capacitive dividers of the priorart are not electrically isolated. Separate measurements of allelectrical quantities desired would require too much apparatus in themodule. Synchronization of module transmissions would require a radioreceiver in each module.

SUMMARY OF THE INVENTION

The present invention provides a novel apparatus for measuring thevoltage on a power transmission line. The voltage measuring apparatus ishoused in a removable module that can be placed anywhere along thetransmission line. Unlike conventional line voltage measuring apparatus,e.g., voltage transformers, the present invention is mobile andlightweight. In addition, the circuit configuration of the presentinvention provides an improvement over prior art voltage measuringapparatus that are subject to external conditions.

DISCLOSURE OF THE INVENTION

Referring to FIG. 1, toroidal shaped sensor and transmitter modules 20are mounted on live power conductors 22 by use of a special, detachablehot-stick tool 108 (see FIG. 2) which opens and closes a positivelyactuated hinging and clamping mechanism. Each module contains means forsensing one or more of a plurality of parameters associated with thepower conductor 22 and its surrounding environment. These parametersinclude the temperature of the power conductor 22, the ambient airtemperature near the conductor, the current flowing in the conductor,and the conductor's voltage, frequency, power factor and harmoniccurrents. Other parameters such as wind velocity and direction and solarthermal load could be sensed, if desired. In addition, each module 20contains means for transmitting the sensed information to a localreceiver 24.

Referring to FIG. 3, each toroidal module 20 is configured with an open,spoked area 26 surrounding the mounting hub 28 to permit free aircirculation around the conductor 22 so that the conductor temperature isnot disturbed. The power required to operate the module is collectedfrom the power conductor by coupling its magnetic field to a transformercore encircling the line within the toroid. The signals produced by thevarious sensors are converted to their digital equivalents by the unitelectronics and are transmitted to the ground receiver in periodicbursts of transmission, thus minimizing the average power required.

One or more of these toroidal sensor units, or modules, may be mountedto transmission lines within the capture range of the receiver andoperated simultaneously on the same frequency channel. By slightlyvarying the intervals between transmissions on each module, keeping themintegral numbers without a common factor and limiting the maximum numberof modules in relation to these intervals, the statistical probabilityof interference between transmissions is controlled to an acceptabledegree. Thus, one receiver, ground station 24, can collect data from aplurality of modules 20.

The ground station 24, containing a receiver and its antenna 30, whichprocesses the data received, stores the data until time to send ordeliver it to another location, and provides the communication portindicated at 32 linking the system to such location. The processing ofthe data at the ground station 24 includes provisions for scalingfactors, offsets, curve correction, waveform analysis and correlativeand computational conversion of the data to the forms and parametersdesired for transmission to the host location. The ground stationprocessor is programmed to contain the specific calibration correctionsrequired for each sensor in each module in its own system.

Referring to FIG. 5, the ground stations 24 are connected to the PowerControl Center 54 by appropriate data transmission links 32 (radio, landlines or satellite channels) where the measured data is processed by aDynamic State Estimator which then issues appropriate control signalsover other transmission links 33 to the switchgear 58 at electricalsubstations 44. Thus the power supply to transmission lines may bevaried in accordance with their measured temperatures and measuredelectrical parameters. Similarly, when sensors are located in both theprimary and secondary circuits of power transformers, transformer faultsmay be detected and the power supplied to the transformer controlled bythe Dynamic State Estimator through switchgear.

In one aspect of the invention a Dynamic State Estimator may be locatedat one or more substations to control the supply of electrical power tothe transformers located there or to perform other local controlfunctions.

Thus, as shown in FIG. 4, an electrical substation 34 may be totallymonitored by the electrically isolated modules 20 of the invention. Upto 15 of these modules may be connected as shown transmitting to asingle receiver 24. The receiver may have associated therewith localcontrol apparatus 36 for controlling the illustrative transformer bank38 and the electrical switchgear indicated by the small squares 40. Themodules 20 may be mounted to live conductors without the expense andinconvenience of disconnecting any circuits and require no wiring at thesubstation 34. The receiver 24 also transmits via its transmission link32 the information received, from the modules 20 (for determining thetotal state of the electrical substation) to the Central Control Station54 of the electrical delivery system.

The system of the invention is adapted for total monitoring and controlof a bulk electrical power delivery system as illustrated in FIG. 5.Here, modules 20 are located throughout the delivery system monitoringtransformer banks 40 and 42, substations 44 and 46, transmission linesgenerally indicated at 48 and 50, and feeder sections generallyindicated at 52.

A number of modules are preferably located along transmission lines suchas lines 48 and 50, one per phase at each monitoring position. Bymonitoring the temperature of the conductors they indicate theinstantaneous dynamic capacity of the transmission line. Since they arelocated at intervals along the transmission line they can be utilized todetermine the nature and location of faults and thus facilitate morerapid and effective repair.

The ground stations 24 collect the data from their local modules 20 andtransmit it to the Power Control Center 54 on transmission links 33. ThePower Control Center, in turn, controls automatic switching devices 56,58 and 60 to control the system.

As illustrated in FIG. 5, ground station 24 located at transformer bank42 may be utilized to control the power supplied to transformer bank 42via a motorized tap system generally indicated at 62.

As shown in FIG. 6, the module 20 according to the invention comprisestwo halves of a magnetic core 64 and 66, and a power takeoff coil 68,and two spring loaded temperature probes 70 and 72 which contact theconductor and an ambient temperature probe 74.

In order to insure that the case 76 is precisely at the potential of theconductor 22 when the conductors are contacted by the probes 70 and 72,a spring 78 is provided, which engages the conductor 22 and remainsengaged with the conductor and connects it to the case 76 before andduring contact of the probes 70 and 72 with the conductor.Alternatively, or simultaneously, contact may be maintained throughconductive inputs in the hub 28.

The electrical current in the conductor is measured by a Rogowski coil80 shown in FIG. 7.

The voltage of the conductor is measured by a pair of arcuate capacitorplates 82 in the cover portions of the donut, only one of which is shownin FIGS. 8 and 9. The electronics is contained in sealed boxes 84 withinthe donut 20 as shown in FIG. 10.

Block diagrams of the electronics of the donut 20 are shown in FIGS. 28and 30.

Referring to FIG. 30, the voltage sensing plates 82 are connected to oneof a plurality of input amplifiers generally indicated at 86. The inputamplifier 86 connected to the voltage sensing plates 82 measures thecurrent between them and local ground indicated at 88, which is theelectrical potential of the conductor 22 on which the donut 20 ismounted. Thus the amplifier 86 provides a measure of the current flowingbetween the plates 82 and the earth through a capacitance C₁ (see FIGS.32 and 33). That is, it measures the current collected by the plates 86which would otherwise flow to local ground. This is a direct measure ofthe voltage of the conductor with respect to earth.

As also shown in FIG. 30, the temperature transducers 70, 72, and 74,and Rogowski coil 80 are each connected to one of the input amplifiers86. An additional temperature transducer may be connected to one of thespare amplifiers 86 to measure the temperature of the electronics in thedonut. The outputs of the amplifiers are multiplexed by multiplexer 90and supplied to a digital-to-analog converter and computer generallyindicated at 92, coded by encoder 94, and transmitted by transmitter 96via antenna 98, which may be a patch antenna on the surface of the donutas illustrated in FIG. 3.

As illustrated in the timing diagram of FIG. 34, the current and voltageare sampled by the computer 92 nine times at one-ninth intervals of thecurrent wave form; each measurement being taken in a successive cycle.The computer initially goes through nine cycles to adjust the one-ninthinterval timing period to match the exact frequency of the current atthat time, and then makes the nine measurements. These measurements aretransmitted to the ground station 24 and another computer 334 at theground station (FIG. 62) calculates the current, voltage, power,reactive power, power factor, and harmonics as desired; provides theseto a communications board 106; and thus to a communications link 32.

For a maximum of fifteen donuts for which it is desired to transmitinformation each second or two, the relative transmission intervals canbe chosen to be between 37/60ths and 79/60ths of a second; eachtransmission interval being an integral number of 60ths of a secondwhich do not have a common factor. This form of semi-random transmissionaccording to the invention will insure 76% successful transmission withless than two seconds between successful transmissions from the samedonut in the worst case.

The hot stick mounting tool of the invention generally indicated at 108in FIG. 3 is shown in detail in FIGS. 25, 26, and 27. It comprises aAllen wrench portion 110 and a threaded portion 112, mounted to auniversal generally indicated at 114. Universal 114 is mounted within ashell 116 which in turn is mounted to a conventional hot stick mountingcoupling generally indicated at 118; and thus the hot stick 176.

When the hot stick tool 108, as shown in FIG. 3, is inserted into theopening 122 in the donut 20, the Allen wrench portion engages barrel 124(FIG. 24) which is oppositely threaded on each of its ends 126 and 128.Threaded portion 126 is engaged with a mating threaded portion of acable clamp 130 and threaded portion 128 engages a mating threadedportion 144 of a nut 132. The nut 132 is fixed by means of bosses 134 inplates 136 and 138, mounted to hinge pins 140 and 142 (FIG. 23). Thus,when the hot stick tool 108 is inserted, and barrel 124 rotated in onedirection, cable clamp 130 is brought towards nut 132, while when barrel124 is rotated in the other direction, cable clamp 130 moves away fromnut 132. Threaded portion 144 of nut 132 engages the threaded portion112 of the hot stick tool 108, such that when cable clamp 130 and nut132 are spread apart the threaded portion 112 of the hot stick tool isthreaded into nut 132 so that the donut module 20 may be supported onthe tool 108.

Since hinge pins 140 and 142 are located near the outer edge of thedonut 20 and fixed pins 146 and 148 are affixed to the donut moreinwardly, if the pins 146 and 148 are spread apart, the donut will opento the position shown in FIG. 6 and if the pins 146 and 148 are broughttogether, the donut will close. The pins 142 and 146 and 140 and 148 arejoined by respective ramp arms 150 and 152. When cable clamp 130 isseparated from nut 132, the ramp arms, and thus pins 146 and 148, arespread apart by the wedge portions 154 and 156 of cable clamp 130. Atthe same time the threaded portion 112 of the hot stick tool 108 engagesthe threaded portion 144 of nut 132 so that the donut 20 is securelymounted to the tool 108. A cable 158 passes around pins 146 and 148 andis held in cable clamp 130 by cable terminating caps 160 and 162. Thuswhen cable clamp 130 and nut 132 are brought together, the cable 158pulls fixed pins 146 and 148 together to securely close the donut 20 andclamp it about the conductor 22. Shortly after it is drawn tight, thethreaded portion of the hot stick tool 108 disengages the threadedportion 144 of nut 132 by continued turning in the same direction.

If for any reason the donut 20 cannot be removed from a conductor 22 byusing the hot stick tool 108, another hot stick tool generally indicatedat 164 in FIG. 20 may be used to cut the cable 158. Tool 164 has a file166 mounted thereon for this purpose. It may also be provided with athreaded portion 168 to engage the threaded portion 144 of nut 132 afterthe cable 158 has been severed.

OBJECTS OF THE INVENTION

It is therefore an object of the invention to provide a system andapparatus for monitoring and control of an electric power deliverysystem.

Another object of the invention is to provide such a systempredominantly employing radio transmitting modules mounted to powerconductors.

A further object of the invention is to provide such a system greatlyreducing, if not eliminating, the use of wiring to transmit measurementsat an electrical substation.

Still another object of the invention is to provide such a system fordetermining the state of a substation dynamically.

Yet still another object of the invention is to provide such a systemfor determining the state of an electrical power delivery systemdynamically.

Yet still another object of the invention is to provide such a systemfor determining dynamic thermal line ratings.

A further object of the invention is to provide such a system formonitoring and controlling the status of electrical power stationequipment.

Another object of the invention is to provide such a system wherein thesensors are capable of measuring, as desired, current, voltage,frequency, phase angle, the fourier components of current and voltagefrom which other quantities may be calculated, the temperature of theconductor to which they are attached, or the temperature of the ambientair surrounding the conductor to which they are attached.

Another object of the invention is to provide a state estimator moduleto sense various power quantities including those necessary for dynamicline ratings that can be rapidly, safely and reliably installed andremoved from an energized high voltage transmission facility, up to 345KV line to line.

A further object of the invention is to provide a state estimator modulethat can be installed and removed with standard utility "hot stick"tools with an adaptor tailored for the module and for operation by asingle lineman or robot.

Still another object of the invention is to provide a "hot stick"mountable unit that is light weight, compact in size, can be remotelycalibrated, is toroidal in shape with a metallic housing consisting of acentral hub suitable for various conductor sizes with the "hot stick"tool capable of opening and closing the toroidal housing around theconductor; the hub being provided with ventilating apertures andthermally insulated inserts which grip the transmission line.

A still further object of the invention is to provide a module of theabove character that is brought to conductor potential before delicateelectric equipment contacts the conductor.

Yet another object of the invention is to provide a state estimatormodule that maintains positive engagement with a hot stick mountabletool except when it is "snap shut" around the conductor.

Yet still another object of the invention is to provide a hinge clampfor a module of the above character.

A yet still further object of the invention is to provide a hinge clampof the above character that may be opened by an alternative hot stickmounted tool in case of failure of the hinge clamp.

Another object of the invention is to provide an electrically isolatedvoltage sensor for a state estimator module of the above character.

Still another object of the invention is to provide an unsynchronizedsingle channel radio transmission system for a plurality of modules ofthe above character.

Other objects of the invention will in part be obvious and will in partappear hereinafter. The invention accordingly comprises the functionsand relationship thereof and the features of construction, organizationand arrangement of parts, which will be exemplified in the system andapparatus hereinafter set forth. The scope of the invention is indicatedin the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the inventionreference should be had to the following detailed description taken inconnection with the accompanying drawings, in which:

FIG. 1 is a perspective view of the state estimator module of theinvention installed on an electrical transmission line;

FIG. 2 is a perspective view showing how a state estimator moduleaccording to the invention may be hot stick mounted to a live conductor;

FIG. 3 is a perspective view of a state estimator module according tothe invention mounted to a conductor;

FIG. 4 is a diagrammatic view of a substation totally monitored by meansof the system of the invention;

FIG. 5 is a diagrammatic schematic view of a power deliver systemmonitored and controlled according to the system of the invention;

FIG. 6 is a top view of a state estimator according to the inventionwith the covers thereof removed;

FIG. 7 is a bottom view of the covers of a state estimator moduleaccording to the invention;

FIG. 8 is a top view of one of the covers;

FIG. 9 is a side view of one of the covers, partly in cross section;

FIG. 10 is an enlarged cross sectional view taken along the line 10--10of FIG. 6 with the cover in place;

FIG. 11 is an enlarged cross sectional view taken along the line 11--11of FIG. 6 with the cover in place;

FIG. 12 is an enlarged fragmentary view of the hub portion of the stateestimator module of FIG. 6;

FIG. 13 is a cross sectional view taken along the line 13--13 of FIG.12;

FIG. 14 is an enlarged view of the conductor clamping jaws shown in FIG.12;

FIG. 15 is a cross section taken along the line 15--15 of FIG. 14;

FIG. 16 is a side view showing the inside of one of the jaws shown inFIG. 14;

FIG. 17 is a enlarged perspective view of one of the jaws of FIG. 14;

FIG. 18 is a view of one of the pins of the hinge clamp mechanism of theinvention;

FIG. 19 is a cross sectional view thereof taken along the line 19--19 ofFIG. 18;

FIG. 20 is a fragmented partially diagrammatic top view of the hingeclamp of the invention and the tool utilized to open it if it jams;

FIG. 21 is a top view similar to FIG. 20 showing the hinge clampmechanism of the invention when the state estimator module of theinvention is clamped about a conductor;

FIG. 22 is a view similar to FIG. 21 showing the hinge clamp mechanismwhen the state estimator module of the invention is opened forengagement or removal from a conductor;

FIG. 23 is a fragmentary side view, partially in cross section takenfrom the top of FIG. 22;

FIG. 24 is an exploded cross sectional view of the working mechanism ofthe hinge clamp of the invention;

FIG. 25 is a diagrammatic front view of the hot stick hinge clampoperating tool of the invention;

FIG. 26 is a back view thereof;

FIG. 27 is a side view thereof;

FIG. 28 is a schematic block diagram of the electronics of the stateestimator of the invention;

FIG. 29 is a detailed schematic electrical circuit diagram of the powersupply of the state estimator of the invention;

FIG. 30 is a detailed electrical schematic block diagram of a portion ofthe electronics illustrated in FIG. 28;

FIG. 31, comprising FIGS. 31A through 31D which may be put together asshown in FIG. 31E, is a detailed schematic electrical circuit diagram ofthe electronics shown in FIG. 30;

FIGS. 32 and 33 are schematic electrical circuit diagrams illustratingthe voltage measurement system according to the invention;

FIG. 34 is a timing diagram of the electronics illustrated in FIG. 30;

FIG. 35 shows a sub-routine call as utilized in the flow charts of FIGS.40 through 61;

FIG. 36 is a memory map of the program;

FIG. 37 is a diagram of PIA port assignments of the program;

FIG. 38 is a diagram of the message transmitted by the donuts 20;

FIG. 39 is a diagram of task management of the program;

FIGS. 40 through 61 are flow charts of the subroutines of a program thatmay be utilized in the donuts 20;

FIG. 62 is an overall block diagram of a ground station receiver remoteterminal interface according to the invention;

FIG. 63 is a diagram of a type of substation that may be monitored bythe electronics shown in FIG. 62;

FIG. 64 is a state diagram of a program that may be utilized in thereceiver 24; and

FIGS. 65, 66, 67, and 68 are diagrams of tables and buffers utilized inthe program of FIG. 64.

The same reference characters refer to the same elements throughout theseveral views of the drawings.

BEST MODE FOR CARRYING OUT THE INVENTION The State Estimator ModuleGeneral

The state estimator modules 20 ("Donuts") clamp to a high-tension powerconductor 22 and telemeter power parameters to a ground station 24 (FIG.1). Each module obtains its operating power from the magnetic fieldgenerated by the current flowing in the high-tension conductor 22. Eachmodule is relatively small and shaped like a donut, with a 125/8" majordiameter and a maximum thickness of 43/4". It weighs approximately 16pounds and may be mounted in the field in a matter of minutes using a"hot stick" (FIG. 2).

Typically, three donuts 20 are used on a circuit; one for each phase.Each donut is equipped to measure line current, line to neutral voltage,frequency, phase angle, conductor temperature and ambient temperature.Digital data is transmitted by means of a 950 MHz FM radio link in a5-10 millisecond burst. A microcomputer at the ground station 24processes data from the 3 phase set and calculates any desired powerparameter such as total circuit kilowatts, kilovars, and volt-amps.Individual conductor current and voltage is also available. This datamay then be passed on to a central monitoring host computer (typicallyonce a second) over a data link 32.

One ground station 24 may receive data from as many as 15 donuts 20, allon the same RF frequency (FIG. 4). Each donut transmits with a differentinterval between its successive transmission bursts, ranging fromapproximately 0.3 seconds to 0.7 seconds. Thus, there will be occasionalcollisions, but on the average, greater than 70% of all transmissionswill get through.

Environmental operating conditions include an ambient air temperaturerange of -40° F. to +100° F.; driving rain, sleet, snow, and icebuildup; falling ice from conductor overhead; sun loading; andvibrations of conductors 22.

Current measurements over a range of 80-3000 amperes must be accurate towithin 0.5%. Voltage measurements over a range of 2.4-345 KV (line-line)must be accurate to within 0.5%. Conductor diameters range from 0.5 to 2inches.

All exterior surfaces are rounded and free from sharp edges so as toprevent corona. The module weighs approximately 16 pounds. It isprovided with clamping inserts for different conductor diameters whichare easily removeable and replaceable. The conductor clamping does notdamage the conductor, even after prolonged conductor vibration due tothe use of neoprene conductor facings 170 in the inserts 186 (FIG. 13).

The special hot stick tool 108 is inserted into the donut 20. Turning ofthe hot stick causes the donut to split so that it may be placed over aconductor. Turning the hot stick in the opposite direction causes thedonut to close over a conductor and clamp onto it tightly. The tool 108may then be removed by simply pulling it away. Reinsertion and turningwill open the donut and allow it to be removed from the line.

Conductor temperature probes 70 and 72 (FIG. 6) are spring loadedagainst the conductor when the donut is installed. The contacting tip174 (FIG. 10) is beryllia and inhibits corrosion and yet conducts heatefficiently to the temperature transducer within. It is also anon-conductor of electricity so as not to create a low resistance pathfrom the conductor to the electronics.

The hub and spoke area in the center of the donut 20 and the temperatureprobe placement are designed with as much free space as possible so asnot to affect the temperature of the conductor.

All electronics within the donut are sealed in water-tight compartments84 (FIG. 10).

The radio frequency transmitter power of the donut 20 is typically 100milliwatts. However, it may be as high as 4 watts. The donut 20 isprotected against lightning surges by MOV devices and proper groundingand shielding practice. All analog and digital circuitry is CMOS tominimize power consumption.

No potentiometers or other variable devices are used for calibration indonut 20. All calibration is done by the ground station 24 by scalingfactors recorded in computer memory.

Each donut is jumper programmable for current ranges of 80-3000 amperesor 80-1500 amperes.

Current is measured by using a Rogowski coil 80 (FIG. 7). Voltage ismeasured by two electrically insulated strips of metal 82 (FIG. 8)imbedded flush on the exterior of one face of the donut. These stripsact as one plate of a capacitor at the potential of the conductor. Theother plate is the rest of the universe and is essentially at calibratedground (neutral) potential with respect to the donut. The amount ofcurrent collected by the donut plate from ground is thus proportional tothe potential of the donut and the conductor on which it is mounted.

Power to operate donut electronics is derived from a winding 68 on alaminated iron core 64-66 which surrounds the line conductor. This coreis split to accommodate the opening of the donut when it clamps aroundthe conductor. The top and bottom portions of the aluminum outer casingof the donut are partially insulated from each other so as not to form ashort circuited turn. The insulation is shunted at high frequency bycapacitors 176 (FIG. 10) to insure that the top and bottom portions 76and 81 are at the same radio frequency potential.

The data is transmitted in Manchester code. Each message comprises thelatest measured Fourier components of voltage and current and anothermeasured condition called the auxiliary parameter, as well as anauxiliary parameter number to identify each of the five possibleauxiliary parameters. Thus, each message format is as follows:

    ______________________________________                                        Donut Identification Number                                                                               4 bits                                            Auxiliary Parameter Number  4 bits                                            Voltage Sine Component (Fourier Fundamental)                                                             12 bits                                            Voltage Cosine Component (Fourier Fundamental)                                                           12 bits                                            Current Sine Component (Fourier Fundamental)                                                             12 bits                                            Current Cosine Component (Fourier Fundamental)                                                           12 bits                                            Auxiliary Parameter        12 bits                                            Cyclic Redundancy Check    12 bits                                            ______________________________________                                    

The auxiliary parameter rotates among 5 items on each successivetransmission as follows:

    ______________________________________                                        Auxiliary                                                                     Parameter No. Parameter                                                       ______________________________________                                        0             Conductor Temperature                                           1             Ambient Exterior Temperature                                    2             Check Ground (0 volts nominal)                                  3             Check Voltage (1.25 volts nominal)                              4             Interior Temperature                                            ______________________________________                                    

More specifically, and referring to FIG. 2, the hot stick tool 108 maybe mounted on a conventional hot stick 176 so that the module 20 may bemounted on an energized conductor 22 by a man 178.

In FIG. 3 it can be seen how the hot stick tool 108 provided with anAllen wrench portion 110 and a threaded portion 112 fits within a hole122 provided in the donut 20 mounted on conductor 22. The donutcomprises two bottom portions 76 and two covers, or top portions 81,held together by six bolts 180. Each bottom portion 76 is provided witha top hub 182 and a bottom hub 184 (see also FIG. 13), supported onthree relatively open spokes 185.

Conductor temperature probes 70 and 72 (see also FIG. 6) are alignedwithin opposed spokes 185.

Identical clamping inserts 186 are held within opposed hubs 182 and 184(see FIG. 13) and clamp conductor 22 with hard rubber facings 170provided therein. The tops 81 (FIG. 3) are each provided with an arcuateflat flush conductor 82 insulated from the housing for measuring voltageand one of the bottom portions 76 is provided with a patch antenna 98for transmitting data to the ground station.

Although the top portions 81 are each provided with a non-conductiverubber seal 188 (FIG. 7) and the area around the hinge is closed bycover plates 190, water escape vents are provided in and around theaccess opening 122, which due to the hot stick mounting is always at thelower portion of the donut 20 when installed on a conductor 22.

Now referring to FIG. 6, a hinge mechanism is provided, generallyindicated at 192. It comprises hinge pins 140 and 142, mounted in a topplate 136 and a bottom plate 138 (see FIG. 23). When opening or closing,the bottom portions 76 along with their covers 81 rotate about pins 140and 142. The two halves of the donut 76--76 are drawn together to clampthe conductor by bringing fixed pins 146 and 148 together by means ofcable 158. They are separated by pushing a wedge against wedge arms 150and 152 to separate pins 146 and 148 which are affixed to the bottomportion 76--76.

To make certain that the bottom portions 76--76 of the donut 20 are atthe potential of the conductor, a spring 78 is provided whichcontinuously contacts the conductor during use and contacts it before itcomes in contact with the temperature probes 70 and 72, protecting themagainst arcing.

To insure that the unit comes together precisely, a locating pin 194 andlocating opening 196 are provided. The multi-layer power transformercores 64 and 66 come together with their faces in abutting relationshipwhen the unit is closed. They are spring loaded against each other andmounted for slight relative rotations so that the flat faces, such asthe upper faces 198 shown in FIG. 6 will fit together with a minimum airgap when the unit is closed. The temperature probes 70 and 72 are springloaded so that they press against the conductor when the unit is closed.The ambient probe 74 is provided with a shield 200 covering the hub areaso that it looks at the temperature of the shield 200 rather than thetemperature of the conductor.

The temperature probes 70 and 72 are located in alignment with opposedspokes 185 so as to provide the least amount of wind resistance so thatthe conductor at the probes 70 and 72 will be cooled by the ambient airin substantially the same way as the conductor a distance away from themodule 20.

The ten radio frequency shunting capacitors 176 can also be seen in FIG.6, as well as the patch antenna 98.

Now referring to FIG. 7, a Rogowski coil 80 is affixed to the covers 81by eight brackets 202 and is connected by lead 203 to the electronics inthe bottom portions 76 (FIG. 10). The non-conductive rubber seal 188 maybe seen in FIG. 7, as well as recesses 206 for stainless steel fibercontacting pads 202 which contact the RF shunting capacitors 176 (FIG.10).

Now referring to FIGS. 8 and 9, the capacitor plate 82 can be seenmounted flush with the surface of one of the covers 81. It may also beseen in FIG. 9 how the openings 206-208 for the Rogowski coil areprovided with slots 210 to prevent the formation of a short circuitingpath around it.

Now referring to FIG. 10, the arcuate capacitor plates 82 are insulatedfrom the case 81 by teflon or other non-conducting material 212. Thesurface gap between the capacitor plate 82 and the surface of the case81 is 0.005 inches. The plates 82 are mounted to the tops 81 by means ofscrews 214 passing through insulated bushings 216 and nuts 218, or byother comparable insulated mounting means. Connection between thecapacitor plates 82 and the electronics may be made by means of thescrews 214. A stainless steel wool pad 202 may be seen in FIG. 10connecting to the shunt capacitor 176 which may be in the form of a feedthrough capacitor. The insulating seal 188 is shown next to the shuntcapacitor 176.

The temperature probe 70 comprises an Analog Device AD-590 sensor 220mounted against a beryllia insert 174 which contacts the conductor 22.The three conductors generally indicated at 222 connect the electronicsto the sensor 220 through an MOV 224.

The sensor 220 and beryllia insert 174 are mounted in a probe head 226which in turn is mounted to a generally cylindrical carriage 227 pushedout by spring 228 to force the beryllia insert 174 against theconductor. A rubber boot 229 protects the interior of the probe 70. Theprobe head 226 is formed of an electrical and heat insulating material.The probe 72 is mounted in a cylindrical post 230 which preferably isadjustable in and out of the lower casing 76 for adjustment to engageconductors of differing diameters. The other conductor temperature probe72 is identical.

An electronics box 84 is mounted within each of the two bottom portions76 and top portion 81. The boxes 84 are hermetically sealed. The powerpickup transformer core 66 and its mating transformer core 64 (FIG. 6)in the other half of the module is pressed by leaf spring 232 againstthe mating core 64 and is pushed against post 234 by means of spring 236so that the flat faces 198 of the two cores 64 and 66, shown in FIG. 6,will come together in a flat face to face alignment when the module isclosed.

Referring now to FIG. 11, it can be seen how the end face 238 of thecore 66 passes through the end plate 240 of lower portion 76. Opening242 is provided for electrical wiring connecting the sealed circuitcontainers 84 in both halves of the device. It should be noted howopening 242 is open, again to prevent encircling the wiring.

The opening 244 for the ambient sensor 74 and the opening 246 for theconductor sensor 70 may be seen in FIG. 11. The hubs 182 and 184 andspokes 185 may be seen in FIGS. 10 and 11 although the openings 248 inthe spoke 185 of FIG. 10 are not shown in order that the temperatureprobe 70 may be shown in detail.

Now referring to FIGS. 12 and 13, it can be seen how the clampinginserts 186 fit within the hubs 182 and 184 and how the facings 170 fitwithin the inserts 186. The inserts 186 are made in sets havingdiffering inner diameters to accommodate conductors 22 of differingdiameters.

As shown in FIGS. 15 through 17, the clamping inserts 186 are providedwith alignment tabs 250 which fit into the hubs 182 and 184. Each of theinserts 186 is identical, one being upside down with respect to theother when installed as shown in FIG. 14. Each is provided with a screwhole 252 for screw mounting them within hubs 182 and 184 and areprovided with a raceway 254 for insertion of and to hold the hardconducting neoprene rubber facings 170, which may be of material, havinga hardness of 70 durometer on the Shore A scale. The facings 170 arepreferably filled with a conducting powder, such as graphite, toestablish electrical contact with the conductor 22.

One of the pins 142 of the hinge is shown in FIG. 18. All of the pinsare provided with a non-conducting ceramic coating 256 which may beplasma sprayed thereon, so that the pins do not provide, together withthe plates 136 and 138 of the hinge (FIG. 23), a shorted turn.

Now referring to FIG. 20, an emergency hot stick mountable tool 164 canbe used to open the donut 20 if for any reason the hinge clamp jams.This tool comprises an elongated file 166 used to cut the cable 158.After the cable 158 has been cut, a threaded portion 168 of theemergency tool may be threaded into the thread portion 144 of nut 132(see FIG. 24) to remove the opened donut 20.

Also, in FIG. 20, it can be seen how the cable clamp 130 is providedwith a raised key portion 258 which guides the cable clamp's motion in aguideway opening 260 in the top plate 136. Also, the circular opening262 in the top plate 136 may be seen, in which the boss 134 of nut 132fits to keep it from moving. A similar boss on the bottom of the nut 132fits into a circular opening in bottom plate 138, as does a similar key264 on the bottom of cable clamp 130 fit into a guiding opening inbottom plate 138. The plates 136 and 138 are secured together by bolts266 and 268 and are held apart by spacers 270 and 272 (FIGS. 21 and 23)about the bolts 266 and 268. Cover plate 136 is machined with openings274 and ribs 276 to make it as strong and light as possible.

FIG. 21 shows the hinge clamp mechanism with the top plate 136 removedand the donut 20 closed, the cable 158 pulling pins 146 and 148 tightlytogether.

In FIG. 22 the hinge clamp mechanism is shown with top plate 136 removedand the cable clamp 130 spread apart from the nut 132 by the barrel 124.The wedges 154 and 156 have pushed ramp arms 150 and 154 to spread apartfixed pins 146 and 148, to open the donut.

In FIG. 23 it can be seen how hinge pins 140 and 142 fit into receivingportions 278 and 280 of each bottom portion 76 of the donut 20.Similarly, fixed pins 146 and 148 fit into portions 282 which are shownpartly cut away in FIG. 23. Portions 282 are located closer to thecentral axis of the donut 20 than hinge pins 142.

Also seen in FIG. 23 are the nuts 284 and 286 on the bolts 266 and 268.

As previously described the hot stick tool 108 (FIGS. 25, 26 and 27) formounting to a conventional hot stick 176 comprises a conventional hotstick mounting coupling 118, a barrel portion 116, a universal joint 114which accommodates misalignment of the line of the stick 120 and thereceiving opening 122 (see FIG. 3) in the donut 20. Also seen in FIGS.25, 26, and 27 are the donut engaging Allen wrench portion 110 andthreaded portion 112 of the hot stick tool 108, and the sleeve 116 whichholds the base 288 of the universal 114 rigidly to the mounting 290 forthe hot stick tool mounted portion of the coupling 118.

State Estimator Module Electronics

The state estimator module electronics are shown in their overallconfiguration in FIG. 28. They comprise a power supply 292, digitizingand transmitting electronics 294, sensors indicated by the box 296, andantenna 98.

The center tap 9 of the power pickoff coil 68 is connected to thealuminum shell of the module 20, which in turn is connected directly tothe power conductor 22 by spring 78 and by the conducting facings 170(FIGS. 12 and 13). Thus, the power conductor 22 becomes the local groundas shown at 88 for the electronics 294. The power supply suppliesregulated +5 and -8 volts to the electronics 294 and an additionalswitched 5.75 volts for the transmitter as indicated at 300. Theelectronics 294 provides a transmitter control signal on line 302 tocontrol the power supply to the transmitter. The sensors 296 provideanalog signals as indicated at 304 to the electronics 294. The detailedschematic electrical circuit diagram of the power supply 292 is shown inFIG. 29.

FIG. 30 is a schematic block diagram of the electronics 294. As showntherein, the Rogowski coil 80 is connected to one of a plurality ofinput amplifiers 86 through current range select resistors 306. Thevoltage sensing plates 82 are connected to the uppermost amplifier whichis provided with a capacitor 308 in the feedback circuit which sets gainand provides an amplifier output voltage in phase with line to neutralhigh tension voltage. It also provides integrator action for themeasurement of current the same way as the amplifier connected to theRogowski coil. Thus amplifier 86 connected to the voltage sensing plate82 is a low impedance current measuring means connected between thepower conductor 22 (i.e., ground 88) and the plates 82.

Each of the temperature transducers 72 and 74 is connected to a separateone of the amplifiers 86 as shown. Spare amplifiers are provided formeasurement of additional characteristics such as the interiortemperature of the donut 20. Each of the amplifiers 86 is connected forcomparison with the output of digital analog converter means 310, 2.5volt reference source 312 at comparator 314 by the multiplexer 90 undercontrol of the digital computer 316. The digital computer may be aMotorola CMOS 6805 microprocessor having I/O, RAM, and timer components.A programmable read only memory 318 is connected thereto for storing theprogram. A zero crossing detector 320 detects the zero crossings of thecurrent in the Rogowski coil 80 and provide basic synchronization. Thedonut ID number is selected by jumpers generally indicated at 322. Thedigitized data assembled into appropriate messages is encoded inManchester code by the encoder 94 and supplied to a 950 megahertztransnitter 96 which then supplies it to the antenna 98.

The schematic electrical circuit diagram of the electronics 294 is shownin FIG. 31, comprising FIGS. 31A through 31D which may be put togetherto form FIG. 31 as shown in FIG. 31E. The grounds therein are shown astriangles. A inside the triangle indicates an analog ground and D adigital ground. Both are connected to the common terminal as indicatedin FIGS. 28 and 31C.

The Voltage Sensor

The operation of the voltage sensor may be understood with reference toFIG. 32. We wish to measure the alternating current voltage V_(l)between the conductor 22 and the ground 324. The metal plates 82 formone plate of a capacitive divider between conductor 22 and ground,comprising the equivalent capacitor C1 between ground and plate 82 andequivalent C2 between conductor 22 and the plate 82.

The voltage V_(L) between ground and the conductor 22 is thus dividedacross the equivalent capacitor C1 and C2.

Prior art methods have attempted to measure the potential developedacross capacitance C2. However this capacitance can change value andaffect the accuracy of the measurement. It may also develop a spuriousvoltage across it due to the high electric field in the vicinity of thehigh voltage conductor 22. The low impedance integrating operationalamplifier of the invention, generally indicated at 326, shuntscapacitance C2 and effectively eliminates it from the circuit. Thepotential of plates 82 is therefore made to be the same as that ofconductor 22 through the operational amplifier 326. Now the potentialbetween the plates 82 and ground 324 is the potential V_(L) between theline 22 and the ground 324. Therefore, the current in the capacitance C₁is now directly proportional to the voltage V_(L). Therefore, the lowimpedance integrater connected operational amplifier 326 will provide anAC output voltage exactly proportional to the current in the capacitanceC₁ and thus directly proportional to the high voltage V_(L) on theconductor 22.

Now referring to FIG. 33, all of the circuitry including the integraterconnected operational amplifier 326 is housed within a metal housing 81,which is connected to the conductor 22 via the spring 78. The plates 82are on the outside of the housing 81 and must be electrically insulatedfrom it. The plates 82 cannot protrude from the housing 81 since thiswould invite corona on very high voltage lines. It therefore must eitherbe flush with the surface of the housing 81 or recessed slightly in it.

Unfortunately rain water or snow collecting on the surface will providea path of high dielectric constant shunting the high electric fieldabout the conductor 22 so that the current I₂ to the operationalamplifier 326 will not be equal to the current I₁ in the capacitance C₁.Thus the measurement will be in error.

In order to minimize this effect the width and length of the sensingplates must be made very large in comparison with the width of the gapseparating them from the housing and if any protective coating is usedover the sensing plate it must have no appreciable thickness.Furthermore, the outer surface of the sensing plate must conform, asclosely as possible, with the outer surface of the housing 81.

Thus the sensing plate 82 shown in FIGS. 8, 9, and 10, are made verylong and have gaps to the housing at their ends of only 0.020 inches andgaps 212 along them of 0.005 inches in width. The plates 82 areapproximately 3/8ths of an inch in width, which is of course very muchgreater than the gaps of 0.05 inches and 0.020 inches.

When constructed in this manner, water droplets covering the metallicsensing plate and bridging the adjacent housing do not materially affectthe measurement of V_(L). This is true because:

1. the sensing plate 82 are directly exposed and water overlying themwhich has a high dielectric constant, simply conducts the capacitivecurrent I₁ directly to the plate;

2. the amount of current shunted by water at the gap between the plates82 and the housing 81 is very small in proportion to the amountcollected by the much larger area sensing plates themselves;

3. the alternating current lost through the shunt path across the gapbetween the pates 82 and housing 82 is very small because of the lowinput impedance of the integrater connected operational amplifier 326.

Deriving the Fourier Components of Current and Voltage

Since the state estimator module 20 is mounted in isolation on ahigh-tension transmission line it is desirable to derive as muchinformation as possible from the sensors contained within it with aminimum of complexity and to transmit this raw data to the groundstation 24 (FIG. 1). Calculation of various desired quantities may thenbe made on the ground.

It is therefore convenient to sample and hold both the current andvoltage simultaneously and to send these quantities to the groundsequentially by pulse code modulation.

When it is desired to derive phase and harmonic data rather than merelytransmitting the root mean square of the voltage and current to theground, the shape of the waveforms and their relative phase must betransmitted.

We do this by transmitting Fourier components. We sample the waveform ofboth current and voltage at intervals of 1/9th of a cycle. However,rather than doing this during one cycle, we do this making onemeasurement at each cycle, changing the interval over nine cycles.

The ground station can then easily compute the quantities of interest,for example, RMS amplitude of voltage and current, their relative phaseand harmonic content.

Since current and voltage are sampled simultaneously, their relativephases are the same as the relative phases of the sample sequence. Theharmonic structures are also the same, so that, except for briefphenomena, any desired analysis may be made by the ground station.

The data transmissions take place in a five to ten second millisecondinterval, which is synchronized with the zero crossing of the donut 20.With this information, the relative phase of three phases of atransmission line as shown in FIG. 1 may be derived.

In the embodiment disclosed herein we only compute the fundamentalFourier components of V_(A) and V_(B) and I_(A) and I_(B) which are:##EQU1## where S_(T) equals the total number of samples in the apparatusdisclosed 9, S equals the sample, and V_(S) and I_(S) are the value ofthe measured voltage and current at each sample S. From these the RMSvoltage V and current I may be derived by the formulas:

    V=[(V.sub.a).sup.2 +(V.sub.B).sup.2 ].sup.1/2

    I=[(I.sub.A).sup.2 +(I.sub.B).sup.2 ].sup.1/2

real power is:

    (V.sub.B ×I.sub.B)+(V.sub.A ×I.sub.A)

and reactive power is:

    (V.sub.A ×I.sub.B)-(V.sub.B ×I.sub.A).

If it is desired to have information about the shape of the waveform(that is harmonic data) more samples may be taken and the desiredFourier harmonic components calculated and transmitted.

"Random" Transmissions on a Single Radio Channel

As shown in FIG. 4, a single substation 34 may have as many as fifteendonuts 20 transmitting data to a single receiver 24. Since radioreceivers are expensive and radio frequency channel allocations are hardto obtain, it is desirable to have all units share a single channel. Forweight and economy it is desirable to minimize the equipment in thedonuts 20 at the expense of complication the receiver 24.

Idealy, all donuts 20 transmitting on a single channel would transmit,in turn, in assigned time slots. Unfortunately, the only way tosynchronize them according to the prior art would be to provide themeach with a radio receiver.

Our donuts 20 are programmed to send out short burst transmissions at"random" with respect to each other, and to do so often enought thatoccasional interference between two or more transmissions does notdestroy a significant portion of the data. This is accomplised byassigning to each donut 20 transmitting to a single receiver 24 a fixedtransmission repetition interval so that no synchronization is required.The interval between transmissions of each of the donuts is an integralnumber and these numbers are chosen so that no two have a common factor.

For example, for fifteen donuts, we choose the intervals W measured insixtieths of a second according to the following table:

    ______________________________________                                               Donut Number                                                                            W                                                            ______________________________________                                               0         37                                                                  1         41                                                                  2         43                                                                  3         47                                                                  4         51                                                                  5         53                                                                  6         59                                                                  7         61                                                                  8         64                                                                  9         65                                                                  10        67                                                                  11        71                                                                  12        73                                                                  13        77                                                                  14        79                                                           ______________________________________                                    

It is desirable that the message length be reduced to a bare minimum inorder to minimize simultaneous message transmission. One way weaccomplish this is to transmit "auxiliary" information in repeatingcycles of five transmissions.

Timing of the Measurements and Transmissions

A timing diagram is shown in FIG. 4, where the sine wave is the currentas measured by the Rogowski coil. At zero crossing labeled φ timing isstarted. During the next cycle labled and succeeding cycles through theeighth, the nine successive Fourier measurements I_(S) and V_(S) aremade. During the ninth cycle the period of the previous eight cycles isutilized to define the sampling interval and the Fourier samples of thecurrent and voltage are again taken during the next eight cycles. Thesemeasurements are utilized to compute V_(A), V_(B), I_(A) and I_(B). Atthe end of the next cycle labeled 9 at the φ crossings, twenty-onecycles have occurred. During the followup period of time, up to a totalof W-1 cycles, the program loads shift registers with the identificationnumber of the donut, the auxiliary number, the Fourier components V_(A),V_(B), I_(A), I_(B), the digitized auxiliary parameters and the CRC (acheck sum). At W-1 the transmission 328 begins and takes place over ashort interval of 5 to 10 milliseconds, (approximately 5 milliseconds inthe apparatus disclosed). Then at the φ crossing at the end of the cyclebeginning at W-1, that is after W cycles, the program is reset to φgoing back to the left hand side of the timing diagram of FIG. 34.

In the program discussed below there is a timer labeled Z which is setto φ at the far left, beginning φ cross over. It is reset to Z=21 at theend of the twenty-first cycle, the second nine to the right in FIG. 34.

The Donut Software

Copyright© 1983,

Product Development Services, Incorporated (PDS)

Scope

The state estimator module 20 (sometimes called herein the substationmonitor) is a MC146805E2 microprocessor device.

Introduction

The "Donut" software specification is divided into three major sections,reflecting the three tasks performed by the software. They are:

Data structures,

The background processing that performs the bulk of the "Donut"operations. Included are transmitter control, sample rate timing, analogvalue conversion, and general "housekeeping",

Common utility sub-routines,

The interrupt processing that handles A.C. power zero-crossinginterrupts and maintains the on-board clock which is used for cycletiming, and

The restart processing that occurs whenever the microprocessor isrestarted.

The program listings are found in Appendix A of U.S. Pat. No. 4,689,752,incorporated herein by reference.

Notation Conventions (a) Logic Statements

Program modules are described via flowcharts and an accompanyingnarrative. The flowcharts use standard symbols, and within each symbolis noted the function being performed, and often a detailed logicstatement.

Detailed statements conform to the following conventions:

    ______________________________________                                        IX         Index Register                                                     SP         Stack Pointer                                                      PC         Program Counter                                                    A,B        Register A or B                                                    CC         Condition Codes                                                    Y          Contents of register or contents of                                           memory location Y.                                                 (y)        Contents of memory location addressed                                         by the contents of register or                                                contents of memory location y.                                     A,X        Contents of location whose address is                                         A - IX.                                                            y(m-n)     Bits m-n of the contents of register                                          y or the contents of memory location y.                            a→b a replaces b. The length of the move                                          (one or two bytes) is determined by the                                       longer of a or b.                                                  ______________________________________                                    

For instance:

    ______________________________________                                        ABC→XYZ                                                                           Move the contents of memory location                                          ABC to memory location XYZ.                                        IX→XYZ                                                                            Save the Index Register in location                                           XYZ.                                                               (IX)→XYZ                                                                          Store the contents of the address                                             pointed to by the Index Register in                                           location XYZ.                                                      .0., X→XYZ                                                                        Same as above.                                                     XYZ+2,X→SP                                                                        Move the bytes in location XYZ+2+(IX)                                         and XYZ+3+(IX) to the Stack Pointer.                               IX→(XYZ)                                                                          Store the Index Register in the memory                                        location pointed to by location XYZ.                               (IX)→(XYZ)                                                                        Store the contents of the memory location                                     pointed to by the Index                                                       Register in the memory location                                               pointed to by location XYZ.                                        ABC (2-3)  Bits 2-3 of memory location ABC.                                   ______________________________________                                    

(b) Subroutine Calls

Subroutine calls contain the name of the subroutine, a statement of thesub-outline, a statement of its function, and the flowchart sectionwhich describes it as shown in FIG. 35.

Data Structures

The memory map is shown in FIG. 36, the PIA Definitions in FIG. 37, andthe Data Transmission Format in FIG. 38.

Background Processing

The Background Processing Hierarchy is shown in FIG. 39.

Substation Monitor Mainline (MAIN) FIG. 40

PURPOSE: MAIN is the monitor background processing loop.

ENTRY POINT: MAIN

CALLING SEQUENCE: JMP MAIN (from RESET)

REGISTER STATUS: A, X not preserved.

TABLES USED: None.

CALLED BY: RESET

CALLS: SYNC, HKEEP, GETVAL, COMPUT, CRC12, SHIFT, XMIT

EXCEPTION CONDITIONS: None.

DESCRIPTION: Main calls SYNC to time the AC frequency and compute thesampling rate, HKEEP to perform general initialization, and GETVAL tosample the analog values. COMPUT is called to finish the Fouriercalculations, the watchdog timer is kicked, and CRC12 is called tocalculate the CRC value for the data to be transmitted. SHIFT is calledto load the shift register, XMIT is called to transmit the data to theground station, the watchdog is kicked, and the entire cycle isrepeated.

Synchronize Timing (SYNC) FIG. 41

PURPOSE: SYNC times the AC frequency and calculates the samplinginterval.

ENTRY POINT: SYNC

CALLING SEQUENCE:

JSR SYNC

Return

REGISTER STATUS: A, X no preserved.

TABLES USED: None.

CALLED BY: MAIN

CALLS: DIV3X9

EXCEPTION CONDITIONS: None.

DESCRIPTION: SYNC initializes the zero crossing count and sets the syncmode flag. The sum buffer is cleared for use as a time accumulator, thezero crossing occurred flag is reset, and the cycle counter is set to10. The zero crossing occurred flag is monitored until 10 zero crossinginterrupts have occurred, at which point the time value is moved to thesum buffer. DIV3X2 is called to divide the 10 cycle time by 9, thequotient is saved as the sampling time, the start flag is set, and areturn is executed.

Perform Housekeeping (HKEEP) FIG. 42

PURPOSE: HKEEP performs cycle initialization.

ENTRY POINT: HKEEP

CALLING SEQUENCE:

JSR HKEEP

Return

REGISTER STATUS: A, X nor preserved.

TABLES USED: TIMTBL-Timing Interval Table

CALLED BY: MAIN

CALLS: None.

EXCEPTION CONDITIONS: None.

DESCRIPTION: HKEEP releases the DAC tracking register, clears the sumbuffers, and resets the timing value remainder. The Donut I. D. numberis read and stored in the data buffer, the cycle interval time isretrieved from the TIMTBL based on the I. D. number, and the auxilliarydata I. D. number is bumped. A return is then executed.

Collect All Data (GETVAL) FIG. 43

PURPOSE: GETVAL reads the nine data samples.

ENTRY POINT: GETVAL

CALLING SEQUENCE:

JSR GETVAL

Return

REGISTER STATUS: A, X not preserved.

TABLES USED: None.

CALLED BY: MAIN

CALLS: SAMPLE

EXCEPTION CONDITIONS: None.

DESCRIPTION: GETVAL monitors the time-to-sample flag. When set, the flatis reset, SAMPLE is called to sample the analog values, and the watchdogtimer is kicked. When the cycle has been repeated nine times, a returnis executed.

Read Analog Values (SAMPLE) FIG. 44

PURPOSE: SAMPLE reads and saves the analog values.

ENTRY POINT: SAMPLE

CALLING SEQUENCE:

JSR SAMPLE

Return

REGISTER STATUS: A, X not preserved.

TABLES USED: None.

CALLED BY: GETVAL

CALLS: READAC, SUMS

EXCEPTION CONDITIONS: None.

DESCRIPTION: SAMPLE calls READAC to read the current and voltage valuesand SUMS to update the Fourier sums. A return is executed unless allnine samples have been taken, in which case READAC is called to read theauxilliary data value. The analog value tracking register is released,and a return is executed.

Read DAC/Comparator Circuit (READAC) FIG. 45

PURPOSE: READAC converts the analogs to digital values.

ENTRY POINT: READAC

CALLING SEQUENCE:

JSR READAC

Return

A, X=12 bit value

REGISTER STATUS: A, B, X not preserved.

TABLES USED: None

CALLED BY: SAMPLE

CALLS: None

EXCEPTION CONDITIONS: None

DESCRIPTION:

READAC initializes the trial and incremental values. The trial value iswritten to the DAC as three four-bit values, and the DAC conversion isinitiated. A short register-decrement delay loop allows the DAC time toconvert, the incremental value is divided by two, and the comparatorinput is checked. The incremental value is subtracted/added to the testvalue if the test value was higher/lower than the actual analog value.

When the incremental value reaches zero, the value is converted to truetwo's complement and a return is executed with the value in A, X.

Maintain Fourier Sums (SUMS) FIG. 46

PURPOSE: SUMS multiplies the analog values by the trigonometric valuesof the phase angles and sums the results.

ENTRY POINT: SUMS

CALLING SEQUENCE:

JSR SUMS

Return

REGISTER STATUS: A, X not preserved.

TABLES USED:

COSINE--Table of cosine values

SINES--Table of sine values

CALLED BY: GETVAL

CALLS:

HULT

Local subroutines: ABSVAL, ADDCOS/ADDSIN--FIGS. 47 & 48

EXCEPTION CONDITIONS: None.

DESCRIPTION: SUMS calls ABSVAL to move the absolute value of the analogvalue to the multiply buffer, moves the trig value to the buffer, andcalls MULT to perform the multiplication. ADDCOS or ADDSIN is called toadd the product to the sine and cosine values for both voltage andcurrent.

Perform Data Manipulations (COMPUT) FIG. 49

PURPOSE: COMPUT performs necessary scaling functions.

ENTRY POINT: COMPUT

CALLING SEQUENCE:

JSR COMPUT

Return

REGISTER STATUS: A, X not preserved.

TABLES USED: None.

CALLED BY : MAIN

CALLS: DIVABS, DIV4X2, DIVCNV

EXCEPTION CONDITIONS: None.

DESCRIPTION: COMPUT moves the scale factor to the divide buffer, callsDIVABS to move the absolute value of the fourier sum to the buffer, andcalls DIV4X2 to perform the division. DIVCNV is called to apply theproper sign to the quotient, and the value is moved to the data buffer.This cycle is repeated for each of the four fourier sums, and a returnis executed.

Compute Cyclic Redundancy Check Value (CRC12) FIG. 50

PURPOSE: CRC12 computes the CRC value.

ENTRY POINT: CRC12

CALLING SEQUENCE: JSR CRC12

Return

REGISTER STATUS: A, X not preserved.

TABLES USED: None.

CALLED BY: MAIN

CALLS: Local Subroutine: CPOLY--FIG. 51

EXCEPTION CONDITIONS: None.

DESCRIPTION:

CRC12 sets a counter to the number of bytes in the data buffer,initializes the CRC value, and gets the data buffer start address. Each6 bit group of data is exclusively "or"ed into the CRC value, and CPOLYis called to "or" the resulting value with the polynomial value. Whenall bits have been processed, a return is executed.

CPOLY sets a shift counter for 6 bits. The CRC value is shifted left onebit. If the bit shifted out is a one, the CRC value is exclusively"or"ed with the polynomial value. When 6 bits have been shifted, areturn is executed.

Load Shift Register (SHIFT) FIG. 52

PURPOSE: SHIFT loads the shift register with the data to be transmitted.

ENTRY POINT: SHIFT

CALLING SEQUENCE:

JSR SHIFT

Return

REGISTER STATUS: A, X not preserved.

TABLES USED: None.

CALLED BY: MAIN

CALLS: Local Subroutine: SHIFT4/SHFAGN--FIG. 53

EXCEPTION CONDITIONS: None.

DESCRIPTION:

SHIFT calls SHIFT4 successively to shift four bits of data at a timeinto the shift register, starting with the most significant bit. Whenall twelve-bit values have been shifted in, SHIFT4 and SHFAGN are calledto fill the shift register with trailing zeroes and a return isexecuted.

SHIFT4 shifts the four data bits in A(0-3) into the hardware shiftregister by setting/resetting the data bit and toggling the registerclock bit. When four bits have been shifted, a return is executed.

SHFAGN is a special entry to SHIFT4 which allows the desired bit count(1-4) to be passed in X.

Transmit Data (XMIT) FIG. 54

PURPOSE: XMIT transmits the contents of the shift register to the groundstation.

ENTRY POINT: XMIT

CALLING SEQUENCE:

JSR XMIT

Return

REGISTER STATUS: A, X not preserved.

TABLES USED: None.

CALLED BY: MAIN

CALLS: None.

EXCEPTION CONDITIONS: None.

DESCRIPTION: XMIT monitors the zero-crossing count. When the countreaches the time-to-transmit count, the transmitter is enabled, and aone millisecond warmup delay is executed. The processor clock isinitialized for external oscillator, and the clock value is set to thebit count plus shut-off delay. The Manchester encoder is enabled and thewatchdog timer is kicked while monitoring the clock. When all data hasbeen sent (clock=0), the Manchester encoder and transmitter aredisabled, the timer is reconfigured for its internal oscillator, and areturn is executed.

Double Precision Multiply (MULT) FIG. 55

PURPOSE: MULT Performs a double precision multiply.

ENTRY POINT: MULT

CALLING SEQUENCE:

MLTBUF+1,2=Multiplier

MLTBUF+3,4=Multiplicand

JSR MULT2

Return

MLTBUF+5,6,1,2=Product

REGISTER STATUS: A, X not preserved.

TABLES USED: None

CALLED BY: COMPUT, SUMS

CALLS: None

EXCEPTION CONDITIONS: None

DESCRIPTION: MULT performs a double precision multiplication by shiftinga bit out of the multiplier, successively adding the multiplicand to theproduct, and shifting the product. When finished, the watchdog timer iskicked, and a return is executed.

Get Absolute Value (DIVABS) FIG. 56

PURPOSE: DIVABS gets the absolute value of the value at X and sets thesign flag.

ENTRY POINT: DIVABS

CALLING SEQUENCE:

X=Value Address

JSR DIVABS

Return

ABSIGN=Sign flag ($FF=Negative)

REGISTER STATUS: X is preserved.

TABLES USED: None.

CALLED BY: COMPUT

CALLS: COMP2

EXCEPTION CONDITIONS: None.

DESCRIPTION: DIVABS resets the sign flag and tests the most significantbit of the value at X. If set, COMP2 is called to find the two'scomplement of the four byte value, and the sign flag is set to $FF. Areturn is then executed.

Convert Scaled Value (DIVCNV) FIG. 57

PURPOSE: DIVCNV applies the sign and divides the value by sixteen.

ENTRY POINT: DIVCNV

CALLING SEQUENCE:

X=Value Address

JSR DIVCNV

Return

REGISTER STATUS: A, X not preserved.

TABLES USED: None.

CALLED BY: COMPUT

CALLS: COMP2

EXCEPTION CONDITIONS: None.

DESCRIPTION: DIVCNV tests the sign flag, ABSIGN. If non-zero, COMP2 iscalled to find the two's complement of the four byte value at X. Thevalue is then shifted right four bits, and a return is executed.

Find Two's Complement Value (COMP2) FIG. 58

PURPOSE: COMP2 finds the two's complement value of the value at X.

ENTRY POINT: COMP2

CALLING SEQUENCE:

X=Value Address

JSR COMP2

Return

REGISTER STATUS: X is Preserved.

TABLES USED: None.

CALLED BY: DIVABS, DIVCNV

CALLS: None.

EXCEPTION CONDITIONS: None.

DESCRIPTION: COMP2 complements each byte of the four byte value at X,adds one to the least significant byte, and propagates the carry throughthe remaining bytes.

Process Zero Crossing Interrupts (ZCINT) FIG. 59

PURPOSE: ZCINT processes zero crossing interrupts.

ENTRY POINT: ZCINT

CALLING SEQUENCE:

From IRQ Vector

Return (RTI)

REGISTER STATUS: A, X are preserved.

TABLES USED: None.

CALLED BY: Hardware IRQ Vector

CALLS: None.

EXCEPTION CONDITIONS: None.

DESCRIPTION:

ZCINT tests the cycle start flag. If set, the analog tracking registeris frozen, the cycle start flag is reset, the time-to-sample flag isset, and the clock is set to the 1-1/9 cycle time.

If the start synchronize flag is set, the clock prescaler is reset, theclock is reset to maximum value, and the start synchronize flag isreset.

The elapsed clock time is saved as the last cycle time, thezero-crossing-occurred flag is set, the zero-crossing count is bumped,and a return is executed.

Process Clock Interrupt (CLINT) FIG. 60

PURPOSE: CLINT processes clock interrupts.

ENTRY POINT: CLINT

CALLING SEQUENCE:

From IRQ Vector

Return (RTI)

REGISTER STATUS: A, X are preserved.

TABLES USED: None.

CALLED BY: Hardware Clock IRQ Vector

CALLS: None.

EXCEPTION CONDITIONS: None.

DESCRIPTION: CLINT freezes the analog tracking register, resets theclock IRQ flag, and sets the time-to-sample flag. The cycle timeremainder value is added into the time accumulator. If a carry results,the 1-1/9 cycle time is increased by one. The clock is reset to thecycle time, and a return is executed.

Perform Power-On Reset (RESET) FIG. 61

PURPOSE: RESET performs power-on initialization.

ENTRY POINT: RESET

CALLING SEQUENCE:

From Hardware Reset Vector

JMP MAIN

REGISTER STATUS: A, X not preserved.

TABLES USED: None.

CALLED BY: Hardware Reset Vector

CALLS: MAIN

EXCEPTION CONDITIONS: None.

DESCRIPTION: RESET inhibits interrupts, clears RAM to zeroes, andinitializes the internal clock and PIA's. The initial time values areinitialized, and the Manchester encoder and transmitter are disabled.Interrupts are reallowed, and a jump to the background processing loopis executed.

The Receiver

The receiver 24 at a substation 34 as shown in FIG. 4 receives data fromfifteen donuts.

In FIG. 62 there is shown an overall circuit block diagram for such areceiver 24.

In addition to receiving transmissions from up to fifteen donuts 20, viaits antenna 30 and radio receiver 330, the receiver 24 can also receiveanalog data from up to 48 current transformers and potentialtransformers generally indicated at 332. The receiver 24 is operated bya type 68000 Central Processing Unit 334. The Manchester codedtransmissions from the donuts 20 received by the receiver 330 aretransmitted via line 336 to a communication board 106 and thence on databus 338 to the 68000 CPU 334. The transformer inputs 332 are conditionedin analog board 340 comprising conditioning amplifiers, sample and hold,multiplexing and analog-to-digital conversion circuits under control ofanalog control board 342. The digitized data is supplied on data bus 338to the CPU 334. The CPU 334 is provided with a random access memory 346,a programmable read only memory 348 for storing its program, and anelectrically erasable read only memory 349 for storing the scalingfactors and personality tables.

The central processing unit 334 may be provided with a keyboard 350 anda 16 character single line display 352. It is also provided with anRS232 port 354 for loading and unloading so called personality tablescomprising scaling factors and the like for the donuts 20 and thetransformer inputs 332. The receiver 24 which is sometimes called hereina remote terminal unit interface, supplies data to a remote terminalunit via current loop 356 from an RS232 communications port oncommunications board 106.

The Receiver Software

Copyright © 1983,

Product Development Services, Incorporated (PDS)

Functional Specification of the Receiver

The remote terminal unit may be a Moore MPS-9000-S manufactured by MooreSystems, Inc., 1730 Technology Drive, San Jose, Calif. 95110, modifiedto receive and store a table of digital data each second sent on line357. Unmodified, the MPS-900-S receives inputs from potential andcurrent transformers, temperature sensors and the like at a substation,and converts these measurements to a digital table for transmission to apower control center 54 (FIG. 5) or for use in local substation control.

Simultaneous transmissions from two or more donuts 20 are ignored sincethe garbled message received will not produce a check sum (CRC) thatmatches the check sum as received. The CRC check portion of the circuitis shown at 337.

Overview

An integral part of commercial power generation is monitoring the amountof power delivered to customers and, if necessary, purchase of powerfrom other companies during peak demand periods. It is advantageous tothe power company to be able to make measurements at remote substations,and be able to relay all the measurements to a central point formonitoring. Because of the large voltages and currents involved incommercial power distribution, direct measurement is not feasible.Instead, these values are scaled down to easily measured values throughthe use of Potential Transformers (PT's) for voltage, and CurrentTransformers (CT's) for current. Recently, we have developed anothermeans for monitoring power line voltage and current. This is the RemoteLine Monitor, a donut shaped (hence the nickname "donut") device whichclamps around the power line itself, and transmits the measured valuesto a radio receiver on the ground.

The Remote Terminal Interface (RTI) monitors power line voltage,current, and temperature by means of Potential Transformers (PT's),Current Transformers (CT's), and temperature transducers respectively.These parameters may also be obtained from Remote Line Monitors, or"donuts" which are attached to the power lines themselves. It is the jobof the RTI to receive this data, and in the case of PT's, CT's andtemperature transducers, digitize and analyze the data. This data isthen used to calculate desired output parameters which include voltage,current, temperature, frequency, kilowatt hours, watts, va, and vars,(the last three being measures of power). These values are then sent tothe Remote Terminal Unit (RTU), and are updated once per second.

Data obtained from PT's, CT's, and temperature transducers must bedigitized by the RTI before it can be used. Data obtained in this way istermed "analog" data. Donuts, on the other hand, send their data to theRTI in digital form. For this reason, input received from donuts is saidto be "digital" input. Each donut supplies three parameters, (voltage,current, and temperature) thus it is equivalent to three analog inputs.

Virtually all commercial power systems in the United States today arethree phase systems. There are two configurations used: the 3 conductoror delta configuration, and the 4 conductor or wye configuration. Tocalculate power (va, vars) it is necessary to measure the voltage andcurrent in all but one of the conductors. That one conductor is used asa reference point for all voltages measured. For a delta configuration,voltage and current in two of the three conductors must be measured(only two phases). This is referred to as the two wattmeter method. Itis desirable to use the two wattmeter method whenever possible becauseonly 2 PT's and CT's are required. For a wye configuration however,voltage and current must be measured in all 3 phases. (The fourthconductor is an explicit reference point. No such reference is providedin the delta configuration, so one of the phases must be used instead.)This latter method is known as the three wattmeter method.

The program listings for the receiver remote terminal interface arefound in Appendix B of U.S. Pat. No. 4,689,752, incorporated herein byreference. They comprise a number of subroutines on separately numberedsets of pages. The subroutines are in alphabetical order in Appendix B.At the top of page 1 of each subroutine the name of the subroutine isgiven, (e.g., ACIA at the top of the first page of Appendix B). Theroutine INIT initializes the computer and begins all tasks.

Appendix C of U.S. Pat. No. 4,689,752, incorporated herein by referencecomprises equates and macro definitions used in the system. Those headedSTCEQU are for the system timing controller (an AM9513 chip). Thoseheaded XECEQU are for the Executive program EXEC in Appendix B. Thoseheaded RTIEQU are unique to the remote terminal interface and usedthroughout the programs of Appendix B.

GENERAL

Accuracy: All calculations will be performed to 5 significant digits,representing an accuracy of 0.01% of full scale.

Input ranges:

Analog voltages and currents will be digitized to a 12 bit bipolar valueranging from -2048 to 2047.

Analog temperature will also be digitized to a 12 bit value which may ormay not be bipolar.

All incoming digital data will be 12 bit values ranging from -2048 to2047.

Number of inputs/outputs: There shall be no more than 48 analog inputsand 15 digital inputs, and no more than 64 outputs. The analog inputsmay monitor no more than 5 separate groups. (A group is defined as acircuit whose voltage is used for the frequency reference and powercalculations) The donuts may be used to monitor a maximum of 5additional groups.

Digital inputs: Digital inputs, if used, will be supplied by `donuts`.(see donut documentation)

Scaling Ranges:

1. Range of donut scaling factors will be from 0.5 to 2. In addition,the temperature value may also have an offset from -1024 to +1023 addedto it.

2. Each PT has a scaling factor associated with it. This factor mayrange from 0.5 to 2.0.

3. Each CT has four scaling factors associated with it. These factorsmay each range from 0.5 to 2.0.

Data Acquisition:

Analog data input:

Analog data can come from three sources: Potential Transformers, (PT's),Current Transformers (CT's), or temperature transducers. The order ofsampling will be determined by the outputs desired. (see Data Output)For voltage and current, 9 equally spaced samples must be taken over thespace of a power line voltage cycle for the purposes of data analysis.(see Data Processing). For each voltage group (maximum of 5), a timermust be mainained to provide proper sampling intervals. This timer willbe checked each sampling period and adjusted if necessary. The firstphase of the voltage sampled will be used as the reference for checkingthe sampling period timer.

The input task knows it may begin sampling for a given group of inputs(cluster) when all of the input buffers connected with it are ready forinput. The necessary data is collected from the A/D converter, andstored in the appropriate input buffer. When this sampling is complete,the buffer is marked as unavailable for further input, and made availabefor Fourier analysis. The sampling timer is then adjusted if necessary,and the input task then proceeds to the next group of buffers in theInput Sequence Table.

B. Digital Input:

Input from the `donuts` (if used) is already digitized and analyzed. Itis only necessary to apply a scaling factor (unique for each parameterfrom each donut) to the data, and convert it to 2's complement form.After this has been done, the data is in a suitable form to calculateoutput data.

Donut input is not solicited, but rather is transmitted in a continuousstream to the RTI. When data is received from a donut, the processor isinterrupted. The incoming data is then collected in a local buffer untila full message from a donut is received and validated. If the data isnot valid, the transmission is ignored, and normal processing continues.If the buffer has already received valid input data for this samplingperiod, the transmission is ignored. Otherwise, the new data is movedfrom the receive buffer into the appropriate data buffer, the age countis cleared, is marked as waiting to be processed, and is made availablefor effective value calculations.

C. Analog Input Error Detection/Action: None.

D. Digital Input Error Detection/Action: A Cyclical Redundancy Check(CRC) word will be provided at the end of each donut transmission. Ifthe CRC fails, the last good data transmitted by that particular donutwill be reused. If the output task references the buffer before new datacomes in, the old data will be reused. If a donut should fail more thanN (to be defined) consecutive times, that donut will be considered to bebad, and its data will be reset to zero.

Data Processing

Analog data must be subjected to Fourier transformation to extract thesine and cosine components of the voltage and current prior tocalculating output values. Also, if the input was a voltage, the sineand cosine components must be scaled by a factor between 0.5 and 2.0.This scaling factor is found in the Input Personality Table, and isunique to each input. If the input was a current, the effective valueand the Fourier components must be scaled by one of four factors rangingbetween 0.5 and 2.0. The scale factor used is dependent on the raw valueof the effective current (Ieff). Each current input has a unique set offour factors. These may also be found in the Input Personality Table.

The purpose of Fourier transformation is to extract the peak sine andcosine components of an input waveform. These components are then usedto calculate the amplitude (effective value) of the waveform. For thisapplication, we are only concerned with the components of thefundamental (60 Hz) line frequency.

If the buffer is an analog input buffer, then the 9 samples areanalyzed, yielding the sine and cosine components of the fundamental.The effective value of the waveform is then computed and stored in thebuffer. The buffer is then marked as being ready for more raw data.

If the buffer is a digital (donut) buffer, then only the effectivevoltage and current are computed and stored in the buffer. When thesecalculations are complete, the buffer is marked as being ready for moreraw data.

After the data has been appropriately processed, then the output valuesmay be calculated. Parameters that may be calculated are: voltage,current, kilowatt hours, watts, va, and vars. Also, temperature, andfrequency may be output. (These are measured, not calculatedparameters.)

Error Detection/Action: None.

Data Output

Output data will be transmitted to the host in serial fashion, Data tobe transmitted to the host will be stored in a circular FIFO buffer tobe emptied by the transmission routine which will be interrupt driven.All data must be converted to offset binary and formatted beforetransmission. A new set of output data will be transmitted to the hostonce per second.

When a buffer is ready to be output, the wattage must be calculated (Ifit hasn't been already) and stored in the buffer corresponding to thephase 1 of the current involved in the calculation. When the wattage iscalculated, the kilowatt hour value is updated also. After calculatingpower and updating KWH, the output task will calculate the requestedoutput parameter and output it (if the appropriate buffers to performthe calculation are ready). The output task will then proceed to thenext entry in the Output Personality Table. When the end of the table isreached, all buffers, both analog and digital, are marked as ready foranalysis. In addition, the output task will enable the transmission ofthe block of data just calculated, and wait until the start of the nextone second interval before starting at the top of the table again.

If the second current input specifier in the output table entry is not-1, the parameter will be calculated using the Breaker-and-a-halfmethod. (see glossary)

Error Detection/Action:

If the requested paramater cannot be calculated because the requisitebuffers are not yet ready, and the output buffer is empty, we have afatal error in that we haven't been able to calculate the requisite datain time for transmission. For now we'll just wait until the data doescome along.

RTI Monitoring/Programming

The RTI will be supplied with an integral 16 key keypad, and single line(16 column) display. From this keyboard, the user may:

continuously monitor any particular output value (the display beingupdated once per second).

display all diagnositc error counts.

transmit an upload request to the host thru the auxiliary port.

In addition, the RTI will have the capability to upload/download anyEEPROM based table through the auxiliary port upon request from thehost. All programming of the RTI (configuration and scaling factorentry) will be performed through this link. Communications protocolswill be defined in the design spec.

Error Detection/Action:

When each table is up/down loaded, a 16 bit CRC word is transmitted withit. Should this CRC check fail on down load, the RTI will request aretransmission and the table in EEPROM will not be updated. On upload,it is the responsibility of the host to request a retransmission.

Initialization

A. Various hardware must be initialized prior to start of operation.Presently defined hardware is:

STC (System Timing Controller). The STC consists of 5 independenttimers, any one of which may be selected to generate an interrupt upontiming out. This is used to insure that the analog samples are taken atthe proper time. The STC is made by Advanced Micro Devices, and its partnumber is 9513.

PI/T: Set timer to provide interrupts at one second intervals to signalthe start of data transmission to the host.

ACIA 1: Host interface

4800 baud

Odd parity

1 stop bit

8 data bits

Host interface monitor (RCV half of ACIG 1)

ACIA 2: Auxiliary link

To be defined.

Error Detection/Action: None.

B. Software initialization:

The analog and digital buffers must be initialized at startup time. Alsoat this time, the Input Sequence Table and Cluster Status Masks arebuilt. Finally, the various tasks must be initialized and started.

Equations:

Fourier analysis (voltage and current): ##EQU2## Where s is the samplenumber. Note: sin (s×40°)/4.5 and cos (s×40°)/4.5 are constants, and maybe stored in a table.

Effective voltage (current): ##EQU3## Temperature: no calculation--theinput value is just passed on. Power:

Watts:

per phase: Watts=(Vb×Ib)+(Va×Ia)

Total power: (this applies to Watts, VARS, and VA)

Three phase (wattmeter) method: pwt=(Phase 1 pwr+Phase 2 pwr+Phase 3pwr)/6144

Two phase (wattmeter) method: pwr=(Phase 1 pwr+Phase 2 pwr)/4096 wherepwr may be WATTS, VARS, or VA.

Note: The constants 6144 and 4096 above are included so that full scalevoltage and full scale current will yield full scale power. Properscaling to actual watts, vars, va, or watt-hours will be performed bythe host.

VARS:

VARS=(Ve×Ib)-(Vb×Ia) (per phase)

Total VARS calculated as per total watts above.

VA:

VA=Veff×Ieff

Total VA calculated as per total watts above.

Tables

Input Personality Table: This table is EEPROM based, and binds aspecific input number to an input type (voltage, current, temperature),group 1, phase 1, and set of correction factors. This table is of afixed size and may have no more than 48 entries. Unused entries willhave a value of 0. The values in this table will be determined atinstallation time.

Output Personality Table:

The Output Personality Table is an EEPROM based table which defines eachof the parameters to be output, and which parameters are necessary tocalculate them. The number of entries (up to 64) in the table is uniqueto the site, and is determined at installation time. The entries arearranged in the order in which they are able to be output. There may beno more than 64 entries in this table.

When donuts are used, both voltage and current readings from theselected donut(s) will be used for power (volt-amp) calculations. (ie.using voltage from a donut and current from a CT will not be permitted)

Donuts shall have ID's ranging from 1 to 15. Each installation usingdonuts must start the donut ID's from 1.

Donuts must be used in groups of three. (Their output is suitable onlyfor use in the 3 wattmeter method.) The ID's of the donuts must beconsecutive, the lowest numbered one being assumed to be phase one, andthe highest numbered one will be assumed to be phase 3.

Zero entries in the table will be ignored.

Input Sequence Table: The Input Sequence Table is RAM based, and builtat RTU startup time, based on the Output and Input Personality tables.For each group, this table specifies which inputs must be sampledsimultaneously to calculate the desired outputs. The groups are enteredinto the table in order of their first reference in the OutputPersonality Table. The Input Personality Table is then referenced tofind the input numbers of all phases of a given input type (ie. current)for any group. Each group is terminated by a zero word. The table isterminated by a word set to all ones.

Donut Scale Factor Table: This table is EEPROM based and contains thedonut's group number and scaling factors to be applied to donut inputs.Scale factors are unique to each parameter input from each donut. Inaddition, the temperature input may also have an offset from -1024 to1023 added to it. This offset is added after the scaling factor has beenapplied. The entries are arranged in order of donut ID's.

    ______________________________________                                        Data Formats:                                                                 ______________________________________                                        A. Incoming Donut Data Format:                                                word    bits   function                                                       ______________________________________                                        1       11-8   don't care                                                             7-4    donut id                                                               3-0    aux. id                                                        2       11-0   Va (cosine component of voltage)                               3       11-0   Vb (sine component of voltage)                                 4       11-0   Ia (cosine component of current)                               5       11-0   Ib (sine component of current)                                 6       11-0   Aux                                                            7       11-0   CRC word                                                       ______________________________________                                        B. Host Transmission Format                                                   For data types 0-6:                                                           word    bits   function                                                       ______________________________________                                        1       7-6    always zero                                                            5-0    value #                                                        2       7-6    always one                                                             5-0    MS 6 bits of value                                             3       7-6    always one                                                             5-0    LS 6 bits of value                                             ______________________________________                                        For data type 7 (KWH):                                                        word    bits   function                                                       ______________________________________                                        1       7      always one                                                             6      always zero                                                            5-0    value #                                                        2       7-6    always one                                                             5-0    MS 6 bits of value                                             3       7-6    always one                                                             5-0    LS 6 bits of value                                             ______________________________________                                        C. Upload/Download format:                                                    byte    bits    function                                                      ______________________________________                                        0-4     0-7    sync character - SYN (#16)                                     5       0-7    table I.D. - ASCII digit 0-3 where:                                            0 - I.D. table                                                                1 - Input Personality Table                                                   2 - Output Personality Table                                                  3 - Donut Scale Factor Table                                  6-7     0-7    byte count - # of bytes of table transmitted                   8-N     0-7    table data - N = byte count + 8                                N+1-N+2 0-7    CRC word. CRC includes bytes 5 thru N                          ______________________________________                                    

Fourier constant table: In the Fourier analysis, the values sin(s×40)/4.5 and cos (s×40)/4.5 (where s ranges from 1 to 9) areconstants, and thus may be stored in a table. This avoids needlesscomputation. Each entry will be a 32 bit floating point number. Therewill be 9 entries for each table. (sine and cosine)

Analog Input Buffer: There are 48 of these buffers, one per A/D channel.The number of buffers actually used is installation dependent. Thesebuffers accept raw input from the A/D, and hold the results ofintermediate calculations until output time. The intermediate values arethe cosine and sine components oo the Fourier analysis of the 9 inputsamples, the effective value (computed from these components), totalwattage, watt seconds, and kilowatt hours. The last three parameters areonly defined for Analog Input buffers corresponding to phase 1 CT's.

Digital Input Buffer: There are 16 digital input buffers in the system.The number of buffers actually used is installation dependent. Thesebuffers are similar in function to the analog input buffers, but theirformat is different due to the fact that data from donuts has alreadybeen analyzed, and voltage, current and temperature data are sent fromeach donut, being equivalent to three analog inputs. The data containedin these tables are the cosine and sine components of voltage, cosineand sine components of current, temperature, effective voltage andcurrent, total watts, watt seconds, and kilowatt hours. The last threeparameters are used only in buffers corresponding to donuts connected tophase one of a group:

GLOSSARY

Breaker-and-a-half method: Method used to calculate parameters when thesubstation bus is configured as shown in FIG. 63 Such a configuration iscalled a Ring Bus. In this configuration, any given circuit is fed fromtwo sources. As a result, two CT's are used to calculate the current inthe circuit, one CT on each source. As a result, any parameter requiringcurrent must be calculated in a special way. The currents from eachsource must be summed and then used in the calculation. This is truewhether the effective value (Ieff) is used, or the components (Ia, Ib)are used. To calculate power, then, the results of 3 inputs are nownecessary rather than two as before. Circuit breakers are identified as358.

Circuit: Three (or four) wires whose purpose is to transmit power fromthe power company. Also called a bus.

Cluster: A collection of inputs which must be sampled at the same timedue to phase considerations. (ie. A given voltage group and all thecurrents related to it through the output personality table constitute acluster. Also, an `entry` in the input sequence table)

Current Group: A three phase circuit (3 or 4 conductor) whose current ismeasured. There may be a maximum of 23 current groups.

Donut: Remote power line monitoring device-linked to RTI via radio link.

[: Current (abbr.)

[a: Cosine component of current waveform.

[b: Sine component of current waveform.

Phase:

1. A power carrying wire in a circuit or bus.

2. Time relationship between two signals, (often, voltage and current)usually expressed in degrees or radians. (i.e. The phase relationshipbetween any two phases of a three phase circuit is 120 degrees)

V: Voltage (abbr.)

Va: Cosine component of voltage waveform.

Vb: Sine component of voltage waveform.

VA: Volt Amps--The vector sum of resistive (watts) and reactive power(VARS).

Voltage Group: A three phase circuit (3 or 4 conductor) whose voltage isused both as a frequency reference and as a voltage reference forsubsequent calculations. There may be a maximum of five of these voltagegroups (1 per cluster).

Receiver Operation

A state diagram for the program of the central processing unit 334 ofFIG. 62 of the receiver 24 is shown in FIG. 64. Processing tasks areindicated by the six-sided blocks. Tables stored in the electricallyerasable read only memory 349 are indicated by the elongated oval boxes.Data paths are shown by dotted lines and peripheral interfaces areindicated by zig-zag lines. The transformer inputs 332 and donut input336 are shown in the upper left. The RS232 port 354 is shown in thelower right and the output RS232 port 32 is indicated in the middle ofthe diagram.

The donut scale factor table is shown in FIG. 65. Since donuts arenormally operated in groups of three for three-phased power measurement,word .0. comprises the group number of the donut (GP), followed by thephase number of the donut (PH). The following words are the voltagescale factor, current scale factor, temperature scale factors, andtemperature offset respectively. Temperature offset is an 11 bit value,sign extended to 16 bits. All two word values are a floating point.There is, of course, a separate scale factor table for each of thefifteen donuts provided for. The donut scale factor tables are stored inthe electrically erasable read only memory 349.

FIG. 66 is a table of the digital input buffers. There are sixteenrequired, one to store the received value of each of the fifteen donutsand one to act as a receiver buffer for the serial port of thecommunication board 106.

Word .0. comprises, in addition to the donut ID and a number calledbuffer age, indicating how long since the information in the buffer hasbeen updated; the following flags:

DI(Data In)--Set when all data has been received and is ready foranalysis. Clear when ready for new data.

AC(Analysis Complete)--Set when effective values and temperature scalingcalculations are complete.

VP(Valid Power)--Set if total watts has already been calculated.

IT(Input Type)--Always 3. Identifies this buffer as donut input.

All single word values are 12 bits, sign extended to 16 bits. All doubleword values are floating point. Buffer age is the number of times thisdata has been used. The first buffer (buffer .0.) is used to assembleincoming donut data. Words 14-16 are defined for .0. 1 donuts only. Word.0. in the buffer number .0. is used for the donut status map. Thedigital input buffers are stored in the read only memory 346.

FIG. 67 is the input personality table of which there are 48corresponding to the 48 potential transformer and current transformerinputs. IT identifies the input type which may be voltage, current, ortemperature. Link is the input number of the next phase of this group ofdonuts. It is -1 if there are no other donuts in the group. Correctionfactor number 1 is used for correcting voltage values. Each of the fourcorrection factors corresponds to a range of input values from thecurrent transformers. Again, as with the donuts, the group numberidentifies groups of transformers associated with a single power lineand PH identifies the phase number of the particular transformer. VGidentifies the voltage group that the current is to be associated (thatis, sampled) with. It is used, of course, only when the table is used tostore values from a current transformer. The input personality tablesare stored in the electrically erasable read only memory 349.

48 analog input buffers are provided to store measurements received fromthe 48 current potential transformers. The form of each of these buffersis shown in FIG. 68.

The follow flags are provided:

DI(Data In)--Set when all raw data has been received and sign extended.Clear when buffer is ready for more data.

AC(Analysis Complete)--Set when Fourier analysis and effective valuecomputations are complete.

VP(Valid Power)--Set if total watts value has already been calculated.

IT(Input Type)--.0.=voltage, 1=current, 2=temperature.

Words 1-9 and 10-18 are 12 bit values, sign extended to 16 bits. All 2word values are floating point. Words 16-18 are defined for .0. 1 ofcurrent inputs only. Words 10-18 are undefined for temperature inputs.VP only applies to buffers associated with .0. 1 current inputs. If IT=2(temperature), the first sample will be converted to floating point andstored at offset 1.0..

In operation, transmissions are received randomly from the donuts 20,transmitted in Manchester code to the serial port to the communicationsboard 106. The checked sum (CRC) is calculated and if it agrees with thecheck gum (CRC) received, an interrupt is provided to the centralprocessing unit 334, which then transfers the data to data bus 338. Thecentral processing unit 68000 applies the scale factors and temperatureoffset to the received values, and calculates the Temperature, effectiveVoltage (V_(EFF)), effective Current (I_(EFF)), Scaled Temperature,Total Watts, Watt Seconds and Kilowatt hours from the received data andstores the data in the appropriate Digital Input Buffer in random accessmemory 346.

In the analog board 340, each of the 48 transformer inputs is sampled inturn. After its condition has been converted to digital form, aninterrupt is generated, and the data is supplied to data bus 338. Itshould be noted that the analog board 340 causes the inputs from thepotential and current transformers 332 to be Fourier sampled nine timesjust as current and voltage are sampled in the donuts (see FIG. 34).Thus, the data supplied to the data bus 338 from the analog board 340comprises 9 successive values over nine alternating current cycles.After all nine have been stored in the random access memory 346, and theappropriate correction factors (FIG. 67) applied, the fundamental sineand cosine Fourier components are calculated just as in the donuts 20.

Then the effective value of current or voltage is calculated and, ifappropriate, the Total Watts, Watt Seconds, and Kilowatt hours, and theentire table (FIG. 68) stored in the random access memory 346.

When the receiver 24 is initially set up, the appropriate donut scalefactors (FIG. 65) are loaded through RS232 port 354 into the electricalerasable read only memory 349, and these are used to modify the valuesreceived from the donuts 20 before they are recorded in the digitalinput buffers of the random access memory 346. Similarly, an inputpersonality table (FIG. 67) is stored in the electrical erasable readonly memory 349 corresponding to each of the current and potentialtransformers and this is utilized to apply the appropriate correctionsto the data received by the analog board 340 before it is recorded inthe analog input buffers of the random access memory 346. The scaleddata stored in the digital input buffers and the corrected data storedin the analog input buffers is then assembled into a frame or messagecontaining all of the defined data from all of the donuts 20 and all ofthe transformers 332 and transmitted via transmission link 32 to areceiver which may be the remote terminal interface of the prior art aspreviously described.

The form of the analog-to-digital, multiplexed input sample and holdcircuitry and program in the receiver 24 may be essentially the same asthat in the donut. The same is true for the Fourier componentcalculation program and the calculation of the check sum (CRC). Theprograms are appropriately modified to run in the 68000 centralprocessing unit with its associated memories.

If harmonic data is desired, then higher Fourier harmonics arecalculated in the donuts 20 and transmitted to the receiver 24. Thereceiver then uses the higher harmonic values to calculate the amplitudeof each harmonic it is desired to measure.

The frequency at any donut 20 may be determined, if desired, bymeasuring the time between transmissions received from the donut asthese are an integral multiple (W, see FIG. 34) of the line frequency atthe donut. Alternatively, the donut may employ an accurate quartz clockto measure the time between zero crossings (FIG. 34) and transmit thisfrequency measurement to the receiver.

If desired, power factor may be calculated from the Fourier componentsand stored in the input buffers (FIGS. 66 and 68). Reactive power (Vars)may be calculated from the Fourier components rather than real power(Watts) as selected by an additional flag in each of the Donut ScaleFactor Tables (FIG. 65) and the Input Personality Table (FIG. 67).Alternatively, all of these calculations and others, as well as otherinformation such as frequency, may be stored in expanded Input Buffers(FIGS. 66 and 68).

The electrical erasable read only memory 349 may be unloaded through theRS232 port 354 when desired to check the values stored therein. They mayalso be displayed in the display 352 and entered or changed by means ofthe keyboard 350.

The output from the receiver 24 is a frame of 64 (for example) datavalues from the Input Buffers (FIGS. 66 and 68) chosen by an outputPersonality Table (not shown) stored in the electrically erasable readonly memory 349. This frame of values is transmitted to the Moore remoteterminal unit once each second. The output personality table may bedisplayed on display 352 and entered by keyboard 350 or entered on readout through RS232 port 354.

Practical Application

It will be thus seen that a number of separate novel concepts have beenapplied to develop a practical state estimator module which may beapplied to live power lines; a module which is capable of measuring thetemperature of the power line, the ambient temperature, the voltage andcurrent of the line; the frequency and harmonic content of the line; andtransmits this information to a receiver where power information such asreal and reactive power and power factor may be calculated.

Thus, we have provided a state estimator module which may be installedto all of the live power lines leading to and from a substantion and toboth sides of power transformers in the substation, and thus provide thetotality of information required for complete remote control of thepower station from a power control center, and also provide for localcontrol. Our state estimator modules may be installed on live monitoredcircuits in an existing substation having current and voltagetransformers and our receiver used to collect this totality ofinformation and transmit it to a remote terminal unit and thence to apower system control center.

Some of the important concepts which make this novel system possible arethe metallic toroidal housing for the module (which is a high frequencybut not a low frequency shunt about its contents); the supporting huband spoke means; spring loaded temperature sensors; novel voltagemeasuring means; transmission of Fourier components; random bursttransmission on a single radio channel with the timing between burstsbeing artfully chosen to minimize simultaneous transmissions from two ormore donuts; novel hinge clamp which may be operated by a novel hotstick mounted tool facilitating the mounting of the module to aenergized power conductor; and the concept that such hot stick mountedmodules when distributed throughout a power delivery system, can providefor total automatic dynamic state estimator control.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above circuits, constructionsand systems, without departing from the scope of the invention, it isintended that all matter contained in the above description, or shown inthe accompanying drawings, shall be interpreted as illustrative and notin a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which as amatter of language might be said to fall therebetween.

Having described our invention, what we claim as new and desire tosecure by Letters Patent is:
 1. Apparatus for measuring voltage on anabove ground power line conductor comprising:a generally toroidal shapedhousing removably attached to said above ground conductor; means forelectrically connecting said housing to said conductor, whereby saidhousing and said conductor are at the same potential; a metal platemounted on the surface of said housing, said plate and said housingbeing separated by insulating material; and said plate connected to saidhousing through a low impedance measuring means whereby said plate andsaid housing are at the same potential and whereby an equivalentcapacitor is formed between said plate and ground; said low impedancemeasuring means connected to said plate and said housing comprising anoperational amplifier for measuring current equal to current in saidequivalent capacitor, said current in said equivalent capacitor beingproportional to the voltage on said power line conductor.
 2. Apparatusas defined in claim 1 wherein said operational amplifier includes afeedback capacitor connected between an input of said amplifier and anoutput of said amplifier and wherein said amplifier functions as anintegrator.
 3. Apparatus as defined in claim 2 wherein said output ofsaid amplifier provides an output voltage signal that is proportional tothe current in an equivalent capacitor formed between said plate andground.
 4. Apparatus as defined in claim 1 wherein the length and widthof said plate are very large relative to the width of the separationbetween said plate and said housing.
 5. Apparatus for measuring voltageon a high voltage, above ground power conductor comprising:a metalliccase adjacent to said above ground conductor and in electrical contactwith said conductor; at least one metallic plate located on the surfaceof said case; insulating material separating said plate and said case,whereby a first equivalent capacitor is formed between said plate andground and a second equivalent capacitor is formed between said plateand said conductor; a low impedance current measuring means connectedbetween said plate and said metallic case in electrical contact withsaid conductor whereby said measuring means shunts said second capacitorand the potential between said plate and ground is equal to thepotential between said conductor and ground; said low impedance currentmeasuring means connected to said plate and said case comprising anoperational amplifier for measuring current equal to current in saidfirst equivalent capacitor, said current in said first equivalentcapacitor being proportional to the voltage on said power conductor. 6.Apparatus as defined in claim 5 wherein said operational amplifierincludes a feedback capacitor connected between an input of saidamplifier and an output of said amplifier and wherein said amplifierfunctions as an integrator.
 7. Apparatus as defined in claim 5 whereinsaid low impedance current measuring means provides an output voltagesignal that is proportional to the current in said first equivalentcapacitor.
 8. Apparatus as defined in claim 5 wherein the length andwidth of said plate are very large relative to the width of theseparation between said plate and said housing.
 9. Apparatus as definedin claim 5 wherein said metallic case is generally toroidal in shape andis removably attached to said conductor.